Interleukin-1 alpha (IL-1α) and beta (IL-1β) are prototypic members of a family of immunoregulatory cytokines and have several prominent roles in regulating the immune system. IL-1α and IL-1β bind to the interleukin-1 receptor I (IL-1RI), leading to the engagement of the secondary receptor, interleukin-1 receptor accessory protein (IL-1RAcP). Signaling agonized by IL-1α and IL-1β leads to amplified T cell responses, including the proliferation and survival of naïve T cells and the development of TH17 cells.